An ignition coil is described in U.S. Pat. No. 6,208,231. The ignition coil has a rod-shaped magnetic core which is covered by a disk-shaped cushioning element at at least one end face (FIGS. 8, 9). The cushioning element is used for the compensation of stresses in the axial direction of the magnetic core based on different coefficients of thermal expansion of the different component parts. Furthermore, the magnetic core is surrounded by a flexible element, for instance, a shrink tube. The shrink tube is used for the compensation of stresses in the radial direction. The component parts are situated within a coil shell. During the production of the ignition coil, the ignition coil housing is filled with an insulating resin used as a sealing compound which fills out cracks that may be present in the interior of the ignition coil. During the pouring of the insulating resin, in order to avoid that insulating resin gets into the annular gap between the magnetic core, including the shrinking tube, and the coil shell, an additional closure element is provided which encloses the coil shell at the inner circumference and seals it from the direction of the magnetic core and the shrinking tube. A disadvantage with this is that mounting the closure element means an additional working step, and the closure element requires additional space in the longitudinal direction of the ignition coil. Furthermore, because of its thickness, the shrinking tube requires space which enlarges the diameter of the ignition coil.
It is also known from U.S. Pat. No. 6,208,231 (FIGS. 16, 17) that one may furnish the outer coil shell with a coating which, based on its low adhesive strength to the component parts, makes possible a relative motion of the component parts with respect to one another, and thus a dissipation of stress.
It is also known from German Patent No. DE 299 16 146 that one may coat the magnetic core with a plastic used as a separator, so that the magnetic core does not undergo any bonding with the insulating resin. In this case, the insulating resin fills out the annular space between the magnetic core and the coil shell. This design approach, too, requires an additional working step, because of the application of the separator onto the magnetic core.